Modern downhole drilling techniques may be enhanced via two-way communication between the surface and a bottom hole assembly (BHA). In many drilling operations digital data is continuously streamed from the BHA to the surface at data rates in a range from about 1 to about 20 bits per second (e.g., using mud pulse telemetry or a mud siren). However, known downlinking methods (methods for transmitting information from the surface to the BHA) are generally slow (e.g., on the order of 1 to 2 bits per minute) and discontinuous (e.g., implemented when the drill bit is off bottom or to transmit a discrete command).
While conventional downlinking methods may be implemented while drilling, such an implementation tends to require significant changes (modulation) to the drilling fluid (mud) flow rate and/or the drill string rotation rate which can negatively impact the drilling process. For example, significant changes to the mud flow rate may adversely affect bit cleaning, hole cleaning, directional capability, and BHA power generation. Significant changes to the drill string rotation rate may adversely affect the rate of penetration and drill string dynamics (modes of vibration). Electromagnetic telemetry methods may also sometimes be used; however, these methods can also have bandwidth limitations and may be limited to fields having suitable well depths and formation resistivity. There is thus room in the art for improved downlinking methods, particularly methods that provide for continuous downlinking while drilling without adversely affecting the drilling process.